Bell of the Bovine is a Unique Amulet in Diablo IV Season 15 for All classes. It comes from Season 15 new Unique (Whimsyshire/Liquid Rainbow content) - source not confirmed; Moophisto, The Divine Bovine (World Boss, Divine Bovine Community Challenge) - one guide's Sources tab.
Unique power
Lucky Hit: When you hit an enemy, you have up to a 30% chance to Moo. Lucky Moo: Up to a 50% chance to summon a cow that explodes, dealing [7.5 - 8]× weapon damage as Fire damage. This damage is increased by 50% on Tuesdays.
Affixes
Mondays now count as Tuesdays
Where it drops
Season 15 new Unique (Whimsyshire/Liquid Rainbow content) - source not confirmed
Moophisto, The Divine Bovine (World Boss, Divine Bovine Community Challenge) - one guide's Sources tab